My daughter has to build a miniature working model of a solar greehouse,
including a system that could prevent over-heating. Could anyone help me?
One way to remove heat from your 'solar greenhouse' is to use 'solar
chimneys'. Place these on the top of your greenhouse above the north
wall. They act as solar ovens in that they heat up the air inside of
them and the hot air naturally rises, and as it rises, it pulls air
out of the greenhouse. To build one, just build a box with opennings
at the top and bottom. The back should be a board with the inside
painted black. The other 3 sides should be plastic or glass. It should
be long and tall but thin.
Since the solar chimney pulls air out of your greenhouse, you need a
way to let air into your greenhouse -- put opennings all around the
base of your greenhouse (for your smaller model, you may just want to
have 1 openning). The incoming air will be the temperature of the
outside air. This air will eventually heat up. If this is not cool
enough, You could also 'pre-cool' this air by having a 'mister' at
your air inlet... hence, when the outside air is pulled through the
opennings, it hits the 'mist' and cools down --- much of the mist will
evaporate because evaporation increases with airflow. If you live in a
humid climate, the mister may not be needed. If you wanted to control
when the misting occurs, you will need to get a solenoid valve from
your local Nursery or hardware store. If you want to turn the mister
on automatically during the day, every day, you could also get a
simple 'timer' as well. Instead, if you want to turn on the mister
based on the temperature, you could wire up the solenoid valve through
a common house thermostat. These Solenoid valves usually take 24Vac.
These 'transformers' are readily available as well.
Another way to cool air, especially in humid climates, is be
'condensative' cooling. Hence, you could have a water trough. Run a
relatively large pipe in the trough for the air to pass through (in
the real world, you could use 4 inch diameter rain gutter pipe (the
type without holes in it.). The pipe is hooked to your air inlets
mentioned above, then the pipes are run into and coiled in the water
trough -- except, the other end of the pipe comes out of the trough,
above the water line, inside the greenhouse.. The outside air comes
into the pipe. The pipes surface is cold from the trough, and thus the
air makes contact with the cold surface, and the vapor in the humid
air condenses out leaving the air cooler.